Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the following questions

Throughout history people have always communicated with one another, not only by speech but also by movements of the hands and body. It is, however, only (42) ______ the last few years that these aspects of communication have been studied at all widely. This type of communication is known as body language or non-verbal communication.

People sometimes wonder (43) ______ you can learn how body language works. It is of course possible to read books on the subject but you also need to (44) ______ time observing people’s movements. A railway station is a particular good place for such observation, as here people can be seen openly expressing eagerness, sorrow, delight, impatience and many other human emotions by (45) _____ of movement.

If you turn down the sound on your television set and try to understand (46) _____ is happening simply by watching the picture you will learn even more about communication (47) _____ words. By turning the sound back up every five (48) ______ or so, it is possible to check how accurate your (49) ______ is.

Having studied the art of body language you will have a definite (50) ______ at a boring party. You will be able to sit on your own for the whole evening and thoroughly enjoy yourself by both watching (51) ______ interpreting the body language of all the other people there.Question 42

A. with

B. during

C. for

D. on

Cho các chất sau :

(1) CH₃CH(NH₂)COOH 

(2) CH₂=CH₂

(3) HOCH₂COOH

(4) HCHO và C₆H₅OH

(5) HOCH₂CH₂OH và p-C₆H₄(COOH)₂ 

(6) H₂N[CH₂]₆NH₂ và HOOC[CH₂]₄COOH

Các trường hợp có thể tham gia phản ứng trùng ngưng là

A. (1), (3), (4), (5), (6)

B. (1), (6)

C. (1), (3), (5), (6)

D. (1), (2), (3), (4), (5), (6)

f(x) = 2x + 3

Ta có: 2x + 3 = 0

<=> 2x = 0 - 3

<=> 2x = -3 => không tồn tại x